1. Field of the Invention
The invention relates to a membrane-electrode assembly, and a method of producing the membrane-electrode assembly, and a solid polymer-type fuel cell employing the assembly.
2. Description of the Related Art
A solid polymer-type fuel cell is an example of a conventional fuel cell. FIG. 6 shows an example of the solid polymer-type fuel cell. A solid polymer-type fuel cell 10 includes a membrane-electrode assembly (MEA) 4 in which an anode catalyst layer 2a and a cathodes catalyst layer 2b are layered respectively on opposite sides of an electrolyte membrane 1, and diffusion layers 3, 3 are layered on outer sides of the catalyst layers. Separators 6, 6 each having a gas channel 5 are disposed on opposite sides of the membrane-electrode assembly 4, thus sandwiching the assembly 4.
The electrolyte membrane 1 constituting the membrane-electrode assembly 4 usually has a membrane thickness of about 10 to 30 μm, and thus is weak in terms of strength, and not easy to handle. Therefore, when the membrane-electrode assembly 4 is produced, it is a usual practice to provide a reinforcement frame or a protective layer for reinforcement on an outer peripheral portion of the electrolyte membrane 1. Such a reinforcement frame or a protective layer also performs the function of preventing short-circuit from occurring in a peripheral edge portion of the membrane-electrode assembly 4 due to cross-leak of gas at the time of power generation. Japanese Patent Application Publication No. 2007-109576 (JP-A-2007-109576) describes a membrane-electrode assembly that includes such a reinforcement frame or a protective layer. In this document, the area of the flat surface portion of the electrolyte membrane is a size larger than the area of the flat surface portion of each of the anode-side and cathode-side catalyst layers. A reinforcement frame made up of a thermosetting resin is disposed on regions in the two surfaces of the electrolyte membrane in which the catalyst layers are not formed, and protective layers are provided on portions of the spaces between the electrolyte membrane and the reinforcement frame.
As in the membrane-electrode assembly described in Japanese Patent Application Publication No. 2007-109576 (JP-A-2007-109576), the protective layers and the reinforcement frame formed for the purpose of prevention of short-circuit and reinforcement of the electrolyte membrane in the membrane-electrode assembly are formed by layering on the electrolyte membrane in regions in the electrolyte membrane where no catalyst layer is formed. When this type of membrane-electrode assembly is produced, it is necessary to accurately position the anode-side and cathode-side catalyst layers relative to the electrolyte membrane and accurately position the reinforcement frame and the protective layers relative to the catalyst layer.
A reason for the need for the accurate positioning is that if there is a positional deviation of any one of the foregoing members, there may occur a site where a catalyst layer partially overlaps with the reinforcement layer or a protective layer, or there may occur a site in the electricity generation region where the electrolyte membrane is not covered with a catalyst layer. In the case where the former site occurs, inconvenience may possibly result when a diffusion layer or the like is layered on top of the site, or in the case where the latter site occurs, local ion conduction may possibly occur, causing partial degradation of the electrolyte membrane. Therefore, the production of the membrane-electrode assembly requires careful operations.